Session establishment protocols such as Session Initiation Protocol (SIP) can be used to establish a call between two endpoints. The SIP protocol includes a referral method that allows a transferor to “transfer” a phone call to a transferee. Under the SIP refer method the transferor establishes a consultative call with the transferee to determine whether the transferee will accept a transfer. When the transferee indicates that the transfer is acceptable, the transferor sends a SIP refer message that includes information about the transferee to a transfer target. The SIP refer message elicits a SIP invite sent from the transfer target to the transferee, which establishes a call between the transferee and the transfer target.
When a Private Branch eXchange (PBX) or other network device for the transferee observes the incoming SIP invite, the PBX is unable to recognize that a new call established with the SIP invite is really a continuation of an original call established with the same remote endpoint. The inability of the PBX to correlate the two calls makes it difficult for a business to track efficiency. For example, a customer service center may need to determine how much time was spent addressing a single request from a customer, which may appear as two requests to the PBX when SIP refer method is used. The disclosure that follows solves these and other problems.